use finishInit() properly for all problems

this means that all code which could potentially throw an exception is
moved to this method(). (In particular FluidSystem::init() proved
troublesome in the past.) Besides avoiding segmentation the faults
which stem from exceptions thrown in constructors, this also has the
advantage that simulations which spend a noticable amount of time to
initialize stop at the "correct" place, i.e. after the "Finish init of
the problem" message was printed by the simulator...

examples/problems/fingerproblem.hh

@@ -193,11 +193,7 @@ public:
      */
     FingerProblem(Simulator &simulator)
         : ParentType(simulator)
-    {
-        eps_ = 3e-6;
-
-        temperature_ = 273.15 + 20; // -> 20°C
-    }
+    { }
 
     /*!
      * \name Auxiliary methods
@@ -229,6 +225,10 @@ public:
     {
         ParentType::finishInit();
 
+        eps_ = 3e-6;
+
+        temperature_ = 273.15 + 20; // -> 20°C
+
         FluidSystem::init();
 
         // parameters for the Van Genuchten law of the main imbibition